The present invention relates in general to connectors useful for mounting microelectronic elements and related electronic components, to assemblies made using such connectors and to methods of making such connectors and assemblies, and more particularly, to such connectors having sockets providing low or zero insertion force connection to microelectronic elements and related electronic components.
Modern electronic devices utilize microelectronic elements which include semiconductor chips, commonly referred to as xe2x80x9cintegrated circuitsxe2x80x9d, which incorporate numerous electronic elements. These chips are mounted on substrates which physically support the chips and electrically interconnect each chip with other elements of the circuit. The substrate may be a part of a discrete chip package used to hold a single chip and equipped with terminals for interconnection to external circuit elements. Such substrates may be secured to an external circuit board. Alternatively, in a xe2x80x9chybrid circuitxe2x80x9d one or more chips are mounted directly to a substrate forming a circuit panel arranged to interconnect the chips and the other circuit elements mounted to the substrate. In either case, the chip must be securely held on the substrate and must be provided with reliable electrical interconnection to the substrate. The interconnection between the chip itself and its supporting substrate is commonly referred to as xe2x80x9cfirst levelxe2x80x9d assembly or chip interconnection, as distinguished from the interconnection between the substrate and the larger elements of the circuit, commonly referred to as a xe2x80x9csecond levelxe2x80x9d interconnection.
The structures utilized to provide the first and second level connections must accommodate all of the required electrical interconnections to the chip. The number of connections to external circuit elements, commonly referred to as xe2x80x9cinput-outputxe2x80x9d connections, is determined by the structure and function of the chip. Advanced chips capable of performing numerous functions may require substantial numbers of input-output connections. Accordingly, the size of the chip and substrate assembly is a major concern. The size of each such assembly influences the size of the overall electronic device. More compact assemblies, with smaller distances between chips provide smaller signal transmission delays and hence permit faster operation of the device.
At present, one widely utilized interconnection method is known as flip-chip bonding. In flip-chip bonding, contacts on the front surface of the chip are provided with bump leads such as balls of solder protruding from the front surface of the chip. The substrate has contact pads arranged in an array corresponding to the array of contacts on the chip. The chip, with the solder bump leads, is inverted so that its front surface faces toward the top surface of the substrate, with each contact and solder bump lead on the chip being positioned on the appropriate contact pad of the substrate. The assembly is then heated to liquefy the solder and bond each contact on the chip to the confronting contact pad of the substrate.
Because the flip-chip arrangement does not require leads arranged in a fan-out pattern, it provides a compact assembly. The area of the substrate occupied by the contact pads is approximately the same size as the chip itself. Moreover, in flip-chip bonding, the contacts on the chip may be arranged in a so-called xe2x80x9carea arrayxe2x80x9d covering substantially the entire front face of the chip. Flip-chip bonding is well suited for use with chips having large numbers of input-output contacts. However, assemblies made by flip-chip bonding are quite susceptible to thermal stresses. The solder interconnections are relatively inflexible, and may be subjected to very high stress upon differential expansion of the chip and substrate. These difficulties are particularly pronounced with relatively large chips.
One solution has been the use of sockets or spring-like contacts to connect the solder bump leads to the substrate. As microelectronic chips have decreased in size, the pitch of the solder bump lead interconnections has become finer, requiring a finer pitch on mating sockets. At the same time, the mating sockets must still compensate for pitch error and height error in the solder bump leads on the chip. Such accommodation for solder bump lead location tolerances becomes increasingly more difficult as the sockets are more tightly packed in a connector.
U.S. Pat. No. 5,802,699 and Application No. 08/862,151 filed on May 22, 1997 entitled xe2x80x9cFlexible Connectors For Microelectronic Elementsxe2x80x9d, both assigned to the same assignees as the present application and hereby incorporated by reference herein, disclose sockets having metallic projections arranged circumferentially around a hole for receiving a bump lead. The metallic projections deflect as the solder bump lead is urged into the hole.
Kohn, et al., U.S. Pat. No. 5,199,879 discloses a pin socket having a plurality of deflectable tabs projecting at least partially across an opening. Matsumoto, et al., U.S. Pat. No. 4,893,172 and Noro, et al., U.S. Pat. No. 5,086,337, disclose variants of the flip-chip approach using flexible spring-like elements connected between a chip and a substrate.
Nishiguchi, et al., U.S. Pat. No. 5,196,726 discloses a variant of the flip-chip approach in which non-meltable bump leads on the face of the chip are received in a cup-like sockets on the substrate and bonded therein by a low-melting point material. Beaman, U.S. Pat. No. 4,975,079 discloses a test socket for chips in which dome-shaped contacts on the test substrate are disposed within conical guides. The chip is forced against the substrate so that the solder balls enter the conical guides and engage the dome-shaped pins on the substrate. Enough force is applied so that the dome-shaped pins actually deform the solder balls of the chip.
Rai, et al., U.S. Pat. No. 4,818,728 discloses a first substrate such as a chip with studs or bump leads protruding outwardly and a second substrate with recesses having solder for engaging the bump leads. Malhi, et al., U.S. Pat. No. 5,006,792 discloses a test socket in which a substrate has an exterior ring-like structure and numerous cantilever beams protruding inwardly from the ring-like structure. Contacts are disposed on these cantilever beams so that the same can be resiliently engaged with contacts of a chip when the chip is placed in the socket. Nolan, et al., A Tab Tape-Based Bare Chip Test and Burn Carrier, 1994 ITAP And Flip Chip Proceedings, pp. 173-179 discloses another socket with cantilevered contact fingers for engaging the contacts on a chip; in this case the contact fingers are formed on a flexible tab tape and reinforced by a silicone material so as to provide forcible engagement and a wiping action with the chip contact.
Despite all of these efforts in the art, however, there have still been needs for improved connectors for connecting microelectronic elements and other related electronic components suitable for use in providing first and second level interconnection in the making of modern electronic devices. More particularly, there is an unsolved need for such connectors which include sockets for receiving solder bump leads for electrical connection thereto using low or zero insertion force to prevent any possible damage to the microelectronic element.
The present invention discloses the formation of socket-like structures on a support such as a dielectric sheetlike layer having top and bottom surfaces, and further including patterned metallic layers on the top and bottom surfaces. The resulting two-sided metal laminate may be formed by adhering metal foil to both sides of a dielectric layer, or may be formed by plating or sputtering a metal to both sides of the dielectric layer.
One process for forming a socket-like structure using the two-sided laminate includes initially etching an opening in the top metal layer. The dielectric layer is then etched through the opening typically using a plasma etching process or a laser etching process to provide a through hole. The etching process undercuts the top metal layer in a region surrounding the opening. The exposed dielectric in the through hole is seeded and plated to form a metal layer within the hole connecting the top and bottom metal layers. Finally, the top and bottom metal layers are patterned etched to form the remaining features of the circuit patterns, such as circuit traces, terminals, contact pads and the like.
The resulting socket-like structure has one or more protruding metal tabs or tines on the top surface of the dielectric layer connected to a metal lower feature on the bottom surface of the dielectric layer by the metal layer lining the through hole. The metal tabs or tines overhang the through hole and can deflect with respect to each other and with respect to the lower feature.
The socket-like structure may be used as a side-contact, or zero insertion force socket having a very fine pitch. In one embodiment, the opening in the top metal layer defines one or more tabs or tines and a central clearance region for a solder ball to be inserted. The tabs or tines are connected to the surrounding top metal layer at points near the region where the solder ball is to be inserted, and extend away from the solder ball while extending toward each other as they extend away from their points of attachment. In another embodiment of the present invention, the tabs or tines are attached to the surrounding top metal layer at points remote from the region where the solder ball is inserted, and likewise extend away from each other from their points of attachment.
In either embodiment, the solder ball is freely inserted with zero insertion force into the through hole through the opening in the top metal layer, and then moved laterally towards the tabs or tines. Upon contact with the tabs or tines, the solder ball separates the tabs or tines and wipes against them, scraping away any oxide coating on the tabs or tines and/or the solder ball, and exposing unoxidized metal beneath.
A connector including at least one and preferably a plurality of low or zero insertion force sockets can be used for mounting a microelectronic element to a substrate, such as another microelectronic element and the like. A microelectronic element having an array of solder balls is juxtaposed with a connector having a plurality of sockets arranged in a corresponding array. In accordance with one embodiment, applying a downward force on the microelectronic element forces the solder ball array downward into the corresponding sockets, and causes the dielectric layer of the connector to be deflected downward between lower solder balls that are supporting the connector and which are used to connect the lower features, e.g., contact pads, on the bottom surface of the dielectric layer with the underlying substrate. Such an arrangement wherein a sheetlike member is supported by and deflects between an array of lower solder balls is described in the aforementioned U.S. patent application Ser. No. 08/862,151.
As the dielectric layer is deflected downward between the lower solder balls, the upper surface of the dielectric layer is compressed, forcing the upper features, e.g., metal contacts, surrounding the sockets to close on the solder balls of the microelectronic element, thereby making contact with the solder ball array.
In accordance with another embodiment of the present invention, the microelectronic element is moved downward so that the solder balls of the solder ball array enter the corresponding array of sockets. A lateral force is then applied to the microelectronic element in order to move the solder ball array with respect to the array of sockets, thereby making contact between each solder ball and one or more of the tabs or tines of each socket. A spacer having holes corresponding to the solder ball array may be used between the microelectronic element and the connector.
In another embodiment of a socket having radially inwardly extending upper features such as tabs or tines, the solder balls of the solder ball array may be larger than the space between the tabs or tines, so that contact is made upon insertion of the solder balls into the sockets. This arrangement may also be combined with a deflectable dielectric layer in order to close the tabs or tines on the solder balls after insertion due to deflection of the dielectric layer and compression of the top layer of the connector. Various patterns of the metal contact pads formed from the top metal layer may be used to enhance the compression of the top layer of the connector in order to cause the tabs or tines to move radially inward and contact the solder balls.
In accordance with another embodiment of the present invention there is described a connector for mounting a microelectronic element thereto, the connector comprising a sheetlike body having a first major surface for facing the microelectronic element and a second major surface, the body including at least one hole extending between the first and second major surfaces, a generally laminar first contact secured to the first major surface of the body having an opening in registration with the hole, the first contact including at least one projection overlying a portion of the hole, the opening constructed for receiving a bump lead on the microelectronic element without engagement with the projection, whereby a microelectronic element can be mounted to the connector by superimposing the microelectronic element on the first major surface of the body so that the bump lead protrudes through the opening into the hole and upon lateral movement of the bump lead within the hole engages the projection for electrical connection thereto.
In accordance with another embodiment of the present invention there is described an electronic assembly comprising a connector as previously constructed, and a microelectronic element having at least one bump lead protruding therefrom and extending into the hole within the body, the microelectronic element being mounted on the first major surface of the connector upon lateral movement of the bump lead within the hole into engagement with the projection for electrical connection thereto.
In accordance with another embodiment of the present invention there is described a method of making connection to a microelectronic element having at least one bump lead thereon, the method comprising the steps of superimposing the microelectronic element on a top surface of a sheetlike body having at least one hole receiving the bump lead therein, the body including a projection secured to the surface of the body and extending overlying a portion of the hole, and displacing the bump lead laterally within the hole into engagement with the projection.
In accordance with another embodiment of the present invention there is described a connector for mounting a microelectronic element to a substrate, the connector comprising a sheetlike dielectric body having a first major surface for facing the microelectronic element and a second major surface for facing the substrate, the body including a plurality of holes extending between the first and second major surfaces arranged in an array corresponding to an array of bump leads on the microelectronic element, an array of generally laminar first contacts secured to the first major surface of the body each having an opening in registration with a corresponding one of the holes, each of the first contacts including at least one sheetlike projection overlying a portion of a corresponding one of the holes, an array of generally laminar second contacts secured to the second major surface of the body in registration with and overlying the holes, the second contacts forming the holes within a blind end adjacent the second major surface of the body, and a conductive layer lining the interior walls of the holes between the first and second contacts, whereby a microelectronic element can be connected to the substrate by superimposing the microelectronic element on the first major surface of the body so that the bump leads on the microelectronic element protrude into the holes for electrical connection to the projection and by connecting the second contacts with conductive elements on the substrate.
In accordance with another embodiment of the present invention there is described an electronic assembly comprising a connector as previously constructed, and a microelectronic element having a plurality of bump leads protruding therefrom arranged in an array corresponding to the array of the holes, the microelectronic element being mounted on the first major surface of the connector such that the bump leads protrude into the holes within the body and are connected to the projection.
In accordance with another embodiment of the present invention there is described a method of making connection to a microelectronic element having an array of bump leads thereon, said method comprising the steps of providing a connector as previously constructed, superimposing the microelectronic element on the first major surface of the body with the bump leads being received in corresponding ones of the holes, and displacing the bump leads laterally within the holes into engagement with a corresponding one of the projections for electrical connection thereto.